BUILDING C++/CLI PROGRAMS in C#.NET

Generation Data Matrix 2d barcode in C#.NET BUILDING C++/CLI PROGRAMS

There are times when you may want to omit the using namespace statements, and simply use the fully qualified name. You will introduce ambiguities if you use two or more namespaces that define the same identifiers. To disambiguate these, you need to fully qualify the names using the scope operator (::), as in Listing 3-3. Listing 3-3. Using the Scope Operator // using_directive2.cpp #using "System.Windows.Forms.dll" int main() { System::Windows::Forms::MessageBox::Show("Hello World!"); } The rule is the same as in classic C++, but I mention it here to emphasize the #using directive is distinct from the using namespace directive, and you may often use both. If you are used to .NET programming in C# or Visual Basic .NET, you are used to providing references on the compile command line or in the Visual Studio project system. If you are using C++, you don t need to reference the assembly on the command line if you reference the assembly via the #using directive. However, you can use the /FU (Force Using) compiler option to reference assemblies via the command line without a #using directive in the code. cl.exe mycode.cpp /FUmylibrary.dll You can also set the /FU compiler option in the Visual C++ development environment. The name of the property is Force #using in the Advanced section of the C/C++ property pages.

You may want to separate your code into different dynamically linked libraries. Let s look at how to use types from one assembly in another in the simplest possible example. Compile the code in Listing 3-4 using the /LD option to generate a DLL. This DLL is a CLR assembly just as was the executable created in a previous section. Listing 3-4. A Trivial Public Class // file1.cpp public ref class R { };

As mentioned, we must add the keyword public at the class level to make this type visible in another assembly (see Listing 3-5). Listing 3-5. Using Our Trivial Class from Another Assembly // file2.cpp #using "file1.dll" // We'll define a function, so we can see it in the metadata later. void F() { R r; } int main() {} Without the keyword public, the type R will not be visible to the code in file2.cpp. Compile file2.cpp with the usual options for managed code (just /clr or /clr:pure will do) to generate an executable assembly file2.exe.

It s possible to set up a special relationship between assemblies that is rather like the friend keyword in classic C++. Such assemblies are called friend assemblies. To reference a friend assembly, use the as_friend modifier in the #using directive. #using "myfriend.dll" as_friend The assembly that s referenced needs to have an assembly attribute. You ll read about attributes in detail in 10, but for now you can just add the following line anywhere in the assembly source code (let s say this is in the source code for myfriend.dll). Typically, this would go in the AssemblyInfo.cpp file in a Visual Studio project: [assembly:InternalsVisibleTo("friend_assembly_filename")]; This line means that an assembly called friend_assembly_filename.dll or friend_assembly_filename.exe is allowed to use the as_friend modifier when referencing myfriend.dll. When an assembly has the special friend relationship, all types at global scope, and any global functions, are accessible to the friend assembly.

The InternalsVisibleTo attribute is an example of an assembly attribute. As you saw in 2, attributes in general specify metadata that can be applied to program elements. If the word assembly is specified in square brackets, the attribute applies to the entire assembly. Most of the metadata in the manifest can be set via assembly attributes.

Most of the CLR project types provided by Visual C++ are created with a file called AssemblyInfo.cpp that contains assembly attributes, such as the version and the company name. That file might look somewhat like the code in Listing 3-6. Listing 3-6. AssemblyInfo.cpp #include "stdafx.h" using using using using using namespace namespace namespace namespace namespace System; System::Reflection; System::Runtime::CompilerServices; System::Runtime::InteropServices; System::Security::Permissions;

// // General Information about an assembly is controlled through the following // set of attributes. Change these attribute values to modify the information // associated with an assembly. // [assembly:AssemblyTitleAttribute("CLRConsole1")]; [assembly:AssemblyDescriptionAttribute("")]; [assembly:AssemblyConfigurationAttribute("")]; [assembly:AssemblyCompanyAttribute("MSIT")]; [assembly:AssemblyProductAttribute("CLRConsole1")]; [assembly:AssemblyCopyrightAttribute("Copyright (c) MSIT 2008")]; [assembly:AssemblyTrademarkAttribute("")]; [assembly:AssemblyCultureAttribute("")]; // // Version information for an assembly consists of the following four values: // // Major Version // Minor Version // Build Number // Revision // // You can specify all the value or you can default the Revision and Build Numbers // by using the '*' as shown here: [assembly:AssemblyVersionAttribute("1.0.*")]; [assembly:ComVisible(false)]; [assembly:CLSCompliantAttribute(true)]; [assembly:SecurityPermission(SecurityAction::RequestMinimum, UnmanagedCode = true)];